1. Field of the Invention
This invention relates to laser systems and more particularly to a laser system having a pump laser resonator.
2. Description of the Prior Art
Diode pumped solid state lasers are of interest because of their compact size, long life times and efficient operation. In these types of systems, light from a pump laser is used to excite the solid state laser material (crystal) to lase. The solid state material typically has a strong absorption at the pump laser wavelength, so that a crystal a few millimeters in length efficiently absorbs most of the pump laser output power.
If the solid state material has a weak absorption of the pump laser power, then the laser will have a low overall efficiency. This weak absorption can be caused by a number of factors. If the laser material has a low doping level, then the absorption can be weak because of the low concentration of active lasing ions. In addition, the pump laser may not be tunable to an absorption peak of the laser material. Finally, the solid state laser crystal may be of such a short length that efficient pump light absorption is not possible.
Short length laser crystals are, however, desirable for a number of reasons. Optical storage systems require that the laser size be kept to a minimum. Shorter crystals have less power loss at the lasing wavelength and avoid the scattering and reabsorption problems which occur in longer length crystals. Shorter crystals can also provide laser light at a single frequency, whereas longer crystals have a tendency to produce laser light at a plurality of closely spaced frequencies.
What is needed is a way to increase the pump radiation absorption in a laser system so that smaller crystals can be used.